This invention relates to the art of spring motors and, more particularly, to improvements in connection with the size and operation of spring motors.
Spring motors according to the present invention have improved size and operating characteristics whereby the spring motors find particular utility in conjunction with assisting the elevating and lowering of a variable load such as that provided by a venetian blind type window covering. Accordingly, the invention is illustrated and described herein in connection with a variable load of the foregoing character. At the same time, however, and as will become apparent, spring motors in accordance with the present invention are advantageously operable in conjunction with controlling the displacement of variable loads other than that provided by a venetian blind and, moreover, are advantageously operable in conjunction with assisting or controlling the displacement of uniform loads.
Spring motors of the character to which the present invention is directed are well known and comprise a flat ribbon of spring metal which is prestressed and coiled so as to have a natural or relaxed state in which the spring forms a tightly wound coil disposed on or in a storage or takeup drum. The free end of the coil is attached to the hub of an output or drive drum onto which the spring is backwound by rotating the output drum in a direction to backwind the spring thereon. When the holding force or load by which the spring is backwound on the output drum is released, the curling property of the spring rewinds the latter onto or into the storage drum toward its natural or relaxed state. As is well known, the spring member in such spring motors can be of constant or variable force, depending upon the intended use for the motor. As is further well known, a variable force characteristic can be attained in a number of ways including tapering the thickness and/or width of the spring member between its opposite ends and/or varying the radius of curvature of the spring member along the length thereof.
Spring motors of the foregoing character are used in a variety of applications where it is desired to control the force required to displace a load or object between extended and retracted positions relative to a location at which the spring motor is fixed. Such uses include the unwinding and rewinding of a motor vehicle seat belt as shown, for example, in U.S. Pat. No. 4,429,840 to Chawla et al., and the elevating end lowering of a load supported in suspension such as shown, for example, in U.S. Pat. No. 5,020,032 to Dale et al. In the foregoing and other applications, a control drum which is coaxial with the output drum is attached thereto for rotation therewith, and a belt or cord is wound onto the control drum in a direction which provides for the unwinding of the belt or cord relative to the control drum to rotate the output drum in the direction for winding the spring member thereonto from the storage drum. When the force required for such unwinding is relaxed, the spring member returns to its natural coiled condition whereupon the output drum is rotated by the spring member in the direction to rewind the cord or belt onto the control drum. In conjunction with elevating and lowering a load such as the base or bottom rail and slats of a venetian blind, two cords can be wound on the control drum in opposite directions with the free ends of the cords attached adjacent the opposite ends of the base rail. When the rail is lowered, the two cords unwind from the control drum thus driving the output drum to wind the spring member thereon. Upward displacement of the rail from a lowered position results in the spring member rewinding relative to the storage drum to rotate the output drum and thus the control drum in the direction to rewind the two cords thereunto. In elevating and lowering a suspended load of the foregoing character which is too heavy to provide desired displacement characteristics in connection with the elevating and lowering thereof using a single spring motor, and as an alternative to providing a larger spring motor for the latter purpose, two spring motors of a given size can be operated in unison and each of the two cords can be wound on the control drum of a corresponding one of the two motors.
Spring motors of the foregoing character have a number of disadvantages, none the least of which is the lack of versatility with respect to designing control arrangements which optimize location of the control drum or other control member relative to the spring motor in conjunction with parameters such as space requirements and spring motor location in connection with a particular intended use for the spring motor. For example in this respect, the control drum is coaxial with the output drum of the spring motor thus adding to the space requirement for the spring motor in the direction of the drum axes. In connection with elevating and lowering a load such as a venetian blind wherein the spring motor is mounted in the head rail of the blind with the drum axes perpendicular to the window, coaxial mounting of the cord drum with the drive drum of the spring motor increases the width requirement for the head rail perpendicular to the window at least by the axial width of the cord drum. This not only requires use of additional material in constructing the head rail but also can affect the aesthetics of the venetian blind assembly, especially where the latter is of the mini-blind type wherein the slats are relatively narrow and it is desirable to provide for the width of the head rail to correspond as closely as possible thereto. Further disadvantage resides in the fact that the required mounting of the cord drum or other control drum on the drive drum of the spring motor precludes any selectivity with respect to positional orientation between the control drum and drive drum and, thus, the ability to construct a spring motor or an arrangement of spring motors to operate in unison without particular concern for the location of the control drum relative to the drive drum of a single spring motor or the drive drums of a plurality of such motors arranged to operate in unison. Still further, in conjunction with operating a plurality of spring motors in unison for elevating and lowering a load such as a venetian blind through the use of a pair of cords, prior art spring motor arrangements do not provide for a desired even motion between the component parts of the several motors and, accordingly, do not provide a desired balance with respect to elevating and lowering the load in the absence of the elevating and lowering control force being equally applied to both cords.